They just needed some leg room: New research shows the great
dinosaur die-off made way for mammals to explode in size — some more
massive than several elephants put together.

The
largest land mammal ever: A rhinoceros-like creature, minus the horn,
that stood 18 feet tall, weighed roughly 17 tons and grazed in forests
in what is now Eurasia. It makes the better known woolly mammoth seem a
bit puny.